Telephone transmission system



' June 4, 1935- o. B. JAcoBs TELEPHONE TRANSMISSION SYSTEM Sgm@ Patented June 4, 1935 UNITED STATES 2,003,969 f N TELEPHONE TRANSMISSION vSYSTEM-1 Oliver B. Jacobs, Morristown, l. J., assignor to Bell` Telephone Laboratories, Incorporated, New York, N. Y.a corporation of NewYork Application March 25, 1930, Serial No.' 438,720' 5 claims. (c1. 17a-17o) This invention relates to speech transmission systems which are electrically long and more particularly to such systems as transoceanic cable circuits includingV voice controlled devices.

An object of this invention is to inform a subscriber talking over a long circuit as to the period of time which should elapse before he should expect a reply.

Another object is. to apprise the'talker at. the terminal end of the circuit that the apparatus in the circuit is conditioned for transmitting in a particular direction.

Voice controlled terminal apparatus-.for electricallyrlong telephone systems are generally arranged to transmit signals in Vone direction at a time. AThe voice currents entering the terminal station at once actuate the operating means to transmit the signals to the line. The rst of two subscribers to begin talking controls the circuit either/by having a portion of the voice energy introduced into the controlling apparatus for connecting the circuit in the proper direction for transmission or by causing a courier current' to besent out in advance of the voice currents to prepare the way. for the latter. U. S. Patents to H. A. Barton 1,574,781, issued March 2, 1926; H. D. Arnold 1,565,302 issued December 15, 1925; R. C. Mathes 1,678,188, issued July 24, 1928; and Nyquist 1,674,695, issued July 26, 1928,'disc1ose several such arrangements. .Y v

A difficulty experienced in such systems (for example, experimental circuits setup to simulate transoceanic cable circuits) isthat a talker, awaiting a reply., does not Wait sufciently long for a response, but tends to resume talking before thek apparatus is conditioned for transmitting a reply from the subscriber atv the distant terminal. The longer the time of transmission in such systems, the'greater the difticulty becomes.

In accordance with the present vinvention it is proposed to overcome these difficulties by providing circuit means to impress anV audible signal on the circuit toward the talker at one terminal during the entire time that the circuit is'in the condition undenwhich message waves from theother terminal cannot come through. This gives the talker a means for determining how longto wait Vfor a response. The subscriber will observe that the'tone ceases shortly after he stops talking and that it is not present when he hears Vthe other party talking. The subscriber soon learnsthat speech from the other end cannot be expected to be heard until the tone ceases and his' reaction is'lto vawaitthe cessation of the tone before vexpecting an answer. Y Y' Accordingeto onelfeature of this invention, circuit means may berprovided to prevent'thetone from being heardby the talker except in the interval after he has ceased talking and until the circuit is in the condition under which message waves transmitted from the-other end can come through. Y s 1 Circuits'embodying the invention Vwill now be described in connection with the accompanying drawing: f n

Fig. 1 of s Which'isadiagrammatic circuit of a typical repeater .unit embodying this invention Fig. 2 of which shows a diagrammatic'circuit of a system illustrating a modified form of this invention. fv .Y v

In the arrangement of Fig.'1 there is shown a section of a transmission line L with a terminal two-wayrepeater unit.` Theterminal repeater is of atype well'known in the art... l

The terminal circuit comprises essentially a repeater circuit having amplifiers AE andrAW' connected to the line sections throughV hybrid coils l and Il, the line sections being balanced by networks N and N1.: The usual delay circuit is associated with each 'ampliiien Bridged across the repeater path east in front of the delay circuit is an echo suppressor unit AD. A similar echo suppressor unit A1D1r is bridged acrossy the pathvtransmitting west in front of itsA associated delay circuit.V These. echosuppressors are'of a type well known inthe art, the detailed' arrangements being illustrated for example infU. S. Patent 1,560,544A issued to G. Crisson November l0, 1925' andinclude suitable vacuum tube amplifying and rectifying A'apparatus -for rectiiying the voice currents rtofoperate a relay. Associated with echo "suppressorAD are' relays Rand R1 which operate in the following manner. f When voice -currents are transmitted from Westto east the echo suppressor AD will actuate its relays R and'Rl'in responsevtov the voice currents to short circuit the repeater path transmitting east to west Vso that the repeater is then only capable of transmitting from west to east, and also'to send an audible tonev from sourcevof oscillations ofaudio frequencyGthrough the contacts of relay R back toward the talker over hybridcoil I0.

Y Coil I0 and network N are suitably balanced so that the tone from source-of oscillations G is transmitted toward the Asubscriber only and cannot find its -way back through the amplifier AE into the linelL. VVRelay R is designed in a manner well known in the` art to be -slow in releasing its contacts after the energizing current has been removed from its winding. The time for the release of the relay contacts may be adjusted to the time it takes the apparatus located at all stations between the subscribers to return to normal after a subscriber ceases to talk. In this manner there will be impressed toward the talker an audible tone only during the time the circuit is in condition under which speech waves transmitted from the other terminal cannot come through. Y

Relay R1 has an extra contact I2 which normally short circuits a source of oscillations O.

When the suppressor AD is actuated in responseA to voice currents transmitted from westto east, the contact I2 is opened and the generator O at once transmits oscillations of the frequency of the generator to the line .Lthrough high pass filter HP. 'Ihe courier frequency ,oscillations transmitted by the generator O act as a courier controlling current 'andgare transmitted lover line L for. the purpose of conditioning the rapparatus at theremote terminal (not shown) for the reception of voice currents before the voice currents, which aredelayed by the delay circuit, arrive. Although .one manner of controlling the circuit apparatus has been described, itis to be understood that the scoperof theinvention includes any other meansfor controlling the circuit. The system for transmitting from one subscriber to another mayemploy reversible repeaters, one-way: repeaters, or any type of repeater suitable for use in a toll or long distance circuit.

Referring to Fig. 2, a transmissionline, such as a submarine cable TC, is illustrated schematically as being connected toi a subscriberat terminal station A through intermediate repeater B and cable.V terminal station C. The stations are shown connected together through line sections L which terminate at each station., Station A comprises essentially a repeater circuit having amplifiers AE' and AW' connected to the line sections through hybrid coils H1 and H2 and the balancing networks N1 and N2. Intermediate repeater B is shown having hybrid coils H3 and H4, balancing networks N3 and N4, an echo suppressor unit of a type well known in the art, for example as illustrated in-U. S. Patent 1,560,544 issued to G. Crisson November 10, 1925. vStation C is the cable terminal station for the submarine cable line and comprises hybrid coil Hspbalancing network N5, and apparatus of any type suitable for connecting a line station to a long submarine cable; namely,.the usualampliilers such as one-way amplifiers A"E andAf'Wf, antisinging echo suppressing apparatusetc. ,At this station there is shownrthe preferred'embodiment of this invention-which comprises amplifier rectier AR and relay R" which operates `when voice currents are transmitted from west to east. The amplier rectifier AR may be part of the echo suppressor equipment at the cable terminal station or separate from sucheqiupment. Relay R is designed as a slow release relay and is provided with normally open contacts-to which a source of oscillations of audio frequency GA is connected. When relay R" operates in response to the voice currents transmitted-,from west to east, its contacts close and an audible tone `from G is sent back over the Veast to west path of transmission toward the talker at station A. The tone is prevented from being sent over submarine cable TC by the usual terminal apparatus located at C. This apparatus may comprise a one-way amplier A"W.

When Voice currents are transmitted from west to east, the echo suppressor SE in repeater B will actuate its relay in response to voice currents and thus short circuit the repeater path for east to west transmission so that repeater B is then only capable of transmitting from west to east. When voice currents are transmitted from east to west suppressor SW actuates its relay to short circuit the repeater path from west to east so that the repeater will now only transmit from east to west.

' The usual delay circuits, which may be associated with the repeater path and which are not shown in this diagram since they form no part of` this invention, delay the transmission of the voice currents through a given path for an interval 'of time suiicient to enable the suppressor tov short circuit the opposite path before the voice currents have been transmitted through the hybrid coil or'before reflection currents due to unbalance may be transmitted back over the other path in the opposite direction.

When the west to east currents arrive at cable terminal station C amplifier rectier AR, which is bridged across the west to east path of transmission, actuates relay R" and an audible signal from source of oscillations G' is sent back over east to west path toward the talker at A. Echo suppressor SE at intermediate repeater B, which had previously operated when the west to east currents had arrived at B and had short circuited the east to west path, will prevent the tone from being'heard by the subscriber at station A until the short circuit is removed. When signal transmission from west to east ceases, the apparatus at the stations return to Vtheir normal condition ready for transmission from east to west, the return to the normal condition taking place after a slight interval. Relay R" is designed to have a necessary hang-over interval which will permit a slow release of its contacts after-talking ceases. Thishang-over is sufficient to permit all apparatus between both subscribers to return to normal beforethe contacts of the relay open. During this interval, an audible tone from source G is sent vthrough the contacts of relay R toward the subscriber at station A.

The echo suppressor at B will prevent the tone from being heard by the talker at A until talking from west to east ceases and the echo suppressor relay SEreleases and returns to its normal condition. The tone will then be heard by the subscriber at station A during the interval after he-has ceased talking and echo suppressor relay SE has released. They tone will continue until relayv R" releases, which occurs when all apparatus in, 'thev circuit between the two subscribers has returned to normal.v 'I'his may be of the orderof one-half second, more or less. The echo.y suppressor relay SE and relay R are designed in amanner well known in the art to release their contacts after an interval of time appropriate foruse in a particular circuit.

"The general principles herein disclosed may be embodied in alltypes of two-wire and four-Wire circuits and are applicable to land lines, submarine cables and radio channels. Although the apparatusv at Vonly one terminal has been shown in thedrawing the general principles inherent in the vapparatus described are applicable to both the other terminal of line L and of submarine cable TC. w Y

What is claimed is: Y

V1,. In a system for transmitting message waves between stations, circuit means at one point in the 'Iiiy system under control of the message waves transmitted for impressing an audible signal toward the talker at one terminal station, and circuit means at another point in the system for preventing the signal from being heard by the talker except during the interval after he has ceased talking and until the system is in condition under which message Waves can be transmitted in the opposite direction and received by the terminal station.

2. In a system for transmitting message waves over a speech transmission channel, a terminal station at one end of the channel, first circuit means for impressing an audible signal toward the talker, and second circuit means for preventing the signal from being heard by the talker except during the interval after he has ceased talking and until the system is in the condition under which message waves can be transmitted in the opposite direction and received by the terminal station, both of said circuit means being located at one end of the speech transmission channel.

3. A two-way message transmission system comprising signaling means for informing the sender how long to wait before a reply can be expected to be received, said signaling means including instrumentalities for transmitting an audible tone toward the sender, said instrumentalities including a source of oscillations of audio frequency, and control means for causing the operation of said instrumentalities during the entire time the system is in the condition that a reply can not be received.

4. A two-way message transmission system comprising signaling means for informing the sender how long to wait before a reply can be expected to be received, said signaling means including instrumentalities for transmitting a signal toward the sender, control means for causing the operation of said instrumentalities during the entire time that the system is in the condition that a reply can not be received, and circuit means for preventing the signal from reaching the sender except during the interval after he has ceased transmitting his message and until the system is in the condition that a reply can be received.

5. A two-Way speech transmission system comprising signaling means for informing the talker hoW long to Wait before an answer can be expected to be received, said signaling means including instrumentalities for transmitting an audible signal toward the talker, control means for causing the operation of said instrumentalities during the entire time the system is in the condition that an answer can not be received, and circuit means for preventing the audible signal from being heard by the talker except during the interval after he has ceased talking and until the system' is in the condition that an answer can be received.

OLIVER B. JACOBS. 

